This invention relates generally to an undercarriage of a crawler-type vehicle having multiple track roller bogie unit, more particularly to a hard bottom undercarriage of the crawler-type vehicle which includes a multiple track roller bogie unit, a track frame pivotally mounted on both side of a vehicle body, an idler rotationally mounted to front portion of the track frame so as to provide longitudinal movement thereon only, and a sprocket located to either sides of the vehicle, and further the idler, the sprocket and the track frame are substantially constructed to lined up in straight line.
It is desirable that the track roller disposed most adjacent the idler and the sprocket are respectively required to maintain a proper and good contact with a crawler even when the vehicle is passed over relatively rough terrain. Various methods have been tried to provide so as to achieve these objects. For example, In FIG. 9 is disclosed Japanese patent application No.1998-46233, published patent No. 1999-227643. The track frames 1 resiliently mounted to a pivot shaft 9 fixed to either sides of the vehicle body (not shown), an idler 2 is rotationally mounted at one end portion of the track frame 1 (generally front portion of the vehicle). A sprocket 3 positioned just behind the other end portion of track frame 1 is rotationally mounted adjacent the pivot shaft 9 fixed to either sides of the vehicle body so as to transfer motor drive power to the crawler through transmission and final drive (not shown). Multiple track roller units including track roller 21, 22, 23 are independently moved up and down under the track frame 1 positioned between the idler 2 and the sprocket 3. The crawler 6 encompasses the idler 2, the sprocket and the multiple track rollers 21, 22, 23. These track rollers 21, 22 are rotationally supported at a lower end portion of arms 4, 5 which are mounted at a pin 7 in opposite direction, positioned apart from each other at the bottom of the track frame 1 and pivoted respectively, independently about it. A single pivotal track roller 23 is rotationally supported at lower end portion of an arm 24, which is mounted relative to a pin as pivotal point G1 positioned at the front portion of the track frame 1. When the vehicle is passing over relatively rough terrain, and some portions of the crawler hang down, these track roller units have advantages, because the double bogie track roller units 10a, 10b, 10c, being in engagement with the track rollers 21, 22 and the single track roller 23 also go down and keep proper contacts with the surface of the track shoes, thereby guiding the crawler for a good and quick travel and preventing the flanges of any of track rollers from moving onto the surfaces of the crawler.
However, above-mentioned undercarriage has disadvantages as follows:
Since the bogie track roller units are designed to be mounted in very small space under the track frame 1, each arms 4, 5 supporting the track rollers 21, 22 are respectively limited in length so as to avoid from contacting with the next track rollers on both sides thereof. Therefore, the stroke of travel of the arms 4, 5 are limited. The case may be occurred that when the vehicle is passing over relatively rough terrain, the crawler below adjacent the idler or the sprocket tends to deflect downwardly due to its weight and separate the track roller 21, 22 therefrom. It could be understood that insufficient arms in length travel up and down for a small amount of the track roller travel, resulting in the track rollers not to provide a quick and proper contact with the deflecting portion thereof and in any of the track rollers moving up potentially the surfaces of the track link.
Moreover, when the vehicle goes up a bump, the envelopment along the bump by the crawler is relatively small, because the strokes of the track rollers are not enough. As a result, the track rollers 21, 22 are unable to fully support the vehicle weight. Therefore, when the vehicle has been through the bump and the body of the vehicle goes down, heavy load shock occurs to the track 6, track roller 21,22 and other elements of the vehicle. Such a load shock leads to diminish the durability of the vehicle elements and provide a bad ride of operation.
In other prior art, for example, Japanese patent application No. 1981-177262, published patent No. 1982-107964 is shown in FIG. 11. The first arms 61, 71 are respectively pivoted about the pin 63, 73 (pivot point) positioned at front and rear portion of a track frame 51. Idlers 52a and 52b are respectively rotationally mounted at a first member of the first arms 61, 71. The second arms 62, 72 are respectively rotationally mounted at a second member of the first arms 61, 71. The track rollers 64, 64 and 74, 74 are rotationally supported to both end portions of the second arms 62, 72. The stop portions 65, 75 are respectively formed on a outer and upper end portions of the first arms 61, 71, while the stop members 66, 76 are respectively formed on a front and rear portion of the track frame 51. The stop portions 65, 75 are respectively positioned to contact with the stop members 66, 76 upon upward pivoting of the first arms 61, 71 to limit such pivoting.
While upper portion of the first arm 54 is pivoted about the pins 58 which are located under the track frame 51 and between the track rollers 64, 64 and 74, 74, the other portion thereof is pivotally connected to substantially a central portion of the second arm 55. At either end portions of the second arm 55 are rotationally supported the track rollers 55, 57. The sprocket 53 is rotationally mounted at either sides of the vehicle body and positioned substantially above the rear idler 52b. The crawler 56 encompasses the idlers 52a, 52b the sprocket 53 and the track rollers 57, 64, 74. It will be seen that this track roller unit has the advantages that a total amount of travel combined an amount of the first arm 54 travel with an amount of the second arm 55 travel provide a quick and proper contact to the rail surfaces of the crawler 56 even when the vehicle is passing over relatively rough terrain.
However, when the idlers 52a, 52b are respectively moved up and down in response of the action of the first arms 61, 71, an actual contact area between the track shoe 56 and ground tends to vary. Variation of the actual contact area causes the track rollers to prevent from serving completely as load bearing member. Accordingly, a trouble occurs that resulting frequent slip of the track shoe leads to provide a low tractive force of the vehicle. And also, when the vehicle is traveling backward and goes up a bump, as shown in FIG. 12, the rear idler 52b is urged to push downward by track shoe weight the adjacent above thereof, thereby the track rollers 74,74 associated with the first arm 71 tends to be prevented from reaching to its lowest position.
An amount of the track roller travel most adjacent the front and rear idlers 52a, 52b depend on running condition of the vehicle and balanced condition to the both idlers. Accordingly, the track rollers may be impossible to reaching to its lowest position as described already, result in providing improper contact to the rail surfaces of the track link.
It is strongly desirable that a great amount of the bogy track roller travel improves a flexibility of the track roller unit without being affected by the travel conditions, the balanced relation to the idlers and the like. And it is also desired that the work in a high tractive force is carried out with the track rollers provided with an unchangeable contact area to the ground.
The present invention is directed to overcoming the shortcomings of the prior attempt at improving adaptability to the track shoe, and securing stable contact areas.
It is an object of the present invention to provide in the crawler-type vehicle undercarriage having an idler, the sprocket and the track frame located substantially in a straight line, a multiple bogie track roller unit with which a great amount of the bogy track roller travel improves a flexibility of the track roller unit to the crawler without being affected by the travel conditions, the balanced relation to the idlers and the like, and work with a high tractive force is carried out with the track roller provided an invariable contact areas to the ground.
It is a still further object of the present invention to provide the crawler-type vehicle comprising an undercarriage which includes the idler, the sprocket and the track frame that includes a first arm pivotally mounted at the bottom of the track frame, a second arm pivotally connected to end portion of the first arm, a track roller unit including a first arm pivotally mounted at the bottom of the track frame, a second arm pivotally connected to end portion of the first arm, and track rollers supported to the either end portion of the second arm.
It is a still further object of the present invention to provide in a crawler-type vehicle comprising an undercarriage which includes an idler, the sprocket and the track frame located substantially in a straight line that a first arm pivotally mounted at the bottom of the track frame, the track roller unit most adjacent the sprocket is pivoted about a pivot center of the first arm positioned at the bottom of the track frame, toward the idler relative to a pivot center of the second arm.
It is a still further object of the present invention to provide in a crawler-type vehicle comprising an undercarriage which includes an idler, the sprocket and the track frame located substantially in a straight line that track roller units most adjacent the sprocket and the idler are respectively pivoted about the pivot center of the first arm positioned at the bottom of the track frame and toward the central portion of the track frame relative to the pivot center of the second arm.